Acoustic Echo Cancellers (AECs) are a critical component in every full-duplex, speech communication system. Its purpose is to remove the echo captured by a local microphone when an audio signal is played through a loudspeaker. The audio signal is often referred to as the speaker audio signal. Typically, an AEC is used during full-duplex communication between someone at a so-called near-end location speaking with another person located remotely at a so-called far-end location. When the far-end person speaks, their voice is transmitted to the near-end location and played through one or more loudspeakers positioned therein. The far-end person's speech, as well as near-end sounds (e.g., near-end speech and/or background noise) is then captured by a near-end location microphone. Without an AEC to process the resulting microphone signal, a copy of the far-end speech would be transmitted back to the far-end location and played on a loudspeaker(s) positioned there. Thus, the far-end person would hear a delayed echo of their previous speech. An AEC suppresses the component of the near-end microphone signal corresponding to the captured speaker audio signal, thereby reducing the perceived echo effect at the far-end location.
An AEC is also used in scenarios that involve audio being played through a near-end loudspeaker, but which is generated locally rather than coming from a far-end location. For example, an AEC can be used to cancel the component of a microphone signal corresponding to audio generated or stored on the computer and played through a local loudspeaker (e.g., music, game sounds, and so on).
While an AEC significantly reduces the echo component of the near-end microphone signal, there is often a residual portion leftover, which is often referred to as the residual echo. In many applications, this residual echo is unacceptable and must be further suppressed. One way of accomplishing this task is through the use of residual echo suppression (RES). RES takes the output of the AEC as input, and further suppresses the residual echo.